When to use it
Use it before spending effort on collecting more precise data.
When to be cautious
One-at-a-time sensitivity does not show combined effects or dependence between inputs.
Apply it
Local sensitivity ≈ change in output / change in input
State the base case, input units and perturbation. One-at-a-time sensitivity does not capture interactions.
- Choose plausible ranges and keep the reference case explicit.
- Vary one driver at a time and record the same output measure.
- Test combined scenarios and investigate inputs that change the decision.
An example in practice
A sourcing decision remains stable when travel cost changes but reverses when support demand increases. Improve the support-demand evidence first.
Source & credit
Standard estimating practice; the cited guide documents use rather than claiming invention.
GAO: Cost Estimating and Assessment Guide
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